There is described a device for running a pipe string, more particularly by there being arranged, at a drill-floor opening which is arranged to receive a pipe string, at least two cooperating pipe-handling units, each, independently of the other or in cooperation with the other, arranged to releasably hold the pipe string fixed and to move the pipe string in its axial direction, and also to move a pipe section in the axial direction of the pipe string and rotate the pipe section around the axis of the pipe string.
Through the change from manual to mechanized and remote-operated pipe handling on drilling installations arranged for exploration and production drilling for, inter alia, oil and gas, the efficiency during the insertion or the withdrawal of the drill string, so-called running of the drill string or “tripping”, or the equivalent for other pipe strings, for example casing, has become considerably reduced. While, in manual make-up or break-out, it was normal to handle 60 pipe sections per hour, the capacity has now fallen by half. In deep-water drilling and in the drilling of increasingly longer wells, very long pipe strings are used today, and there is an increased need to reduce the time for insertion and pulling-out and reduce the costs of such operations.
By the techniques of today for inserting a drill string into the borehole, the drill string is constructed step by step from sections consisting of one, two or three joints of pipe. The part of the pipe string which has been moved down into the borehole (or down into a riser connecting the borehole to the surface installation when the drilling takes place at sea) has been hung off in the drill floor by means of a wedge mechanism (slips), and the pipe string is lengthened by a new pipe section being moved from a pipe rack down onto the pipe string and made up by means of a pipe tong while the pipe string is prevented from rotating by it being held fixed, at a portion projecting above the drill floor, by a back-up tong. When a new pipe section has been joined to the pipe string, the drill string is lowered by a length corresponding to that of the added pipe section and the process is repeated. When tripping out, this sequence of operations is reversed.
When the drill string is at a standstill for a pipe section to be added or removed, there is a risk that the drill string may stick in the borehole because of differential pressure in the borehole, or fragments from an open portion of the borehole coming loose and wedging against the drill string and so on. This risk may entail extra time expenditure to loosen the drill string; possibly, the drill string will have to be pulled out for damage to be repaired.
From WO 03/102350, there is known a drill-rig apparatus arranged for assembling and disassembling a well pipe, including a power tong arranged for the rotation of an upper pipe section, a back-up tong arranged for holding an underlying well pipe fixed, and a wedge arrangement arranged in the drill floor and arranged for the drill pipe to be hung off. The power tong and back-up tong can be moved in the axial direction of the well pipe.
CA 2207832 discloses a method of removing, from a well, a rod which is encased in jointed tubing; for example, a rod driving a downhole piston pump. It is described how pipe sections and rod sections, alternately, are broken out of the pipe string and rod, respectively, by means of a back-up tong and a power tong.
From WO2005/056975 is known a power tong with a non-divided drive ring surrounding the vertical centre axis of the drilling centre and the pipe string. The power tong, which cooperates with an underlying back-up tong, is movable in a vertical direction to the position of a pipe joint which is to be broken out or joined.
U.S. Pat. No. 5,060,542 discloses a power tong including three gripping jaws, of which only a combination of two is functional at all times when a pipe string is to be assembled or disassembled. This is achieved by the power tong being vertically movable to position the desired pair of gripping jaws at the pipe joint.
In what follows, the terms “pipe string” and “pipe section” are not restricted to a drill string or casing, but cover all types of pipes that are made up of stands of pipe sections that are joined on a drilling installation and are gradually moved downwards as the length of the pipe increases.